Modern semiconductor electronic devices such as integrated circuit chips are formed by building multiple stacked layers of materials and components on a semiconductor substrate. The semiconductor devices typically incorporate numerous electrically active components which are formed on the substrate. Metal conductor interconnects, which may be made of copper in some embodiments, are formed by various additive patterning and deposition processes such as damascene and dual damascene to electrically couple the active components together by means of circuit paths or traces formed within one or more layers of dielectric material. Modern semiconductor fabrication entails a repetitive sequence of process steps including material deposition (conductive and non-conductive dielectric materials), photolithographic patterning of circuits in the dielectric material, and material removal such as etching and ashing which gradually build the stacked semiconductor device structures.
Chemical-mechanical polishing or planarization (“CMP”) is a technique used in semiconductor fabrication for global planarization of the layers formed on the substrate in order to provide a uniform surface profile or topography upon which successive layers of materials may be built. As well known to those skilled in the art, CMP basically entails use of a polishing apparatus that is supplied with an abrasive chemical slurry which may contain an abrasive such as colloidal silicon dioxide or alumina, deionized water, and chemical solvents or oxidants such as hydrogen peroxide, potassium or ammonium hydroxide. The slurry is typically pumped under pressure to the CMP station by a slurry feed system and applied directly onto the surface of the semiconductor wafer. The slurry is then worked into the wafer surface by a rotating polisher pad or head to polish/plane the surface.
FIG. 1 is a diagram of a known slurry feed system 10 for storing and supplying slurry to a CMP station. As shown in FIG. 1, concentrated slurry is fed from supply drums 11 into a slurry mixing tank 12 where the slurry is mixed and diluted with deionized water and a chemical(s) such as H2O2 (hydrogen peroxide). The quantity of slurry and deionized water fed into the mixing tank 12 are measured using flow meters and/or scales to provide the desired proportions of each in creating the intended slurry blend. The diluted slurry is then piped to a pumping station consisting of two slurry feed pumps 13 arranged in parallel pumping relationship. The feed pumps 13 discharge into a common header and slurry is transferred to a valving switch box 14 comprising a plurality of valving and circuitous interconnecting piping branches for switching the slurry flow path to form two separate slurry supply piping loops A and B as shown. Recirculation piping 17 is provided to return slurry flow back to mixing tanks 12. In this embodiment, there is a second redundant/standby slurry supply system including generally a second slurry mixing tank 12 and parallel set of slurry supply pumps 13 which also feeds slurry to the valving switch box 14. The slurry flows from valve switching box 14 through either piping loops A and B to a valve manifold box (VMB) 15 which supplies slurry from either loops A or B (depending on which is being used) to the CMP station 16 for polishing/planing semiconductor wafers. The quality of the slurry to the CMP station may be monitored by instrumentation 18 operative to measure such slurry parameters as specific gravity and pH.
The foregoing known slurry feed system 10, however, has numerous operational and maintenance drawbacks. With parallel pumping arrangements as shown in FIG. 1, one drawback is that loss of one of the pumps 13 will cause a drop in the pressure and flowrate in the slurry feed system of sufficient magnitude such that the requirements of the CMP station 16 can no longer be met. Therefore, the redundant/standby slurry system 11 must be placed into service and the slurry system with the failed pump must be isolated for repair. The complex pumping and valving arrangement in valving switch box 14 makes this transition difficult to implement for fabrication plant operators when switching from one slurry supply system 11 to the redundant/standby slurry system for either pump repair or whenever routine maintenance of one of the slurry systems is required due to the large number of valves that require opening/closing to implement the switch. Furthermore, the circuitous piping arrangements in valving switch box 14 inherently creates numerous “dead legs” where stagnant flow allows slurry to accumulate and/or solidify. This creates problems with maintaining proper slurry concentrations and quality, in addition to creating potential plugging problems in the piping when the alternate unused loops must be placed into service for switching to the redundant slurry supply system 11.
Another drawback of the conventional slurry feed system 10 shown in FIG. 1 is instrument drift or shifting that occurs with the flow meters and/or scales used to measure the quantities of deionized water, chemicals, and slurry fed to the slurry mixing tank 12. This makes measuring the exact amounts of deionized water and slurry difficult which may adversely affect slurry quality and requires frequent maintenance to recalibrate these measurement instruments.
Another drawback of the conventional slurry feed system 10 shown in FIG. 1 is that the mixing tanks 12 are relatively small and have little reserve capacity such that a single day's supply of slurry for the CMP stations 16 cannot be accommodated by a single mixing tank 12. Accordingly, when one mixing tank 12 runs out of slurry and a new batch must be prepared, this cannot be done without removing the empty mixing tank from service. The slurry feed must be switched to the standby slurry feed system 11, which hopefully already has a batch of dilute slurry prepared and ready to supply the needs of the CMP stations 16. Otherwise, the semiconductor fabrication process is interrupted resulting in production time loss and higher fabrication costs. In addition, switching the slurry supply between mixing tanks in the operating and redundant/standby feed systems 11 must sometimes be done on a daily basis which is cumbersome to implement due to the many valve openings/closings that must be made by an operator in valving switch box 14 as already described above.
An improved slurry feed system is desired that minimizes or eliminates the foregoing problems with conventional slurry feed systems.